We use the perfective will have when we are looking back from a point in time when something will have happened.

By the end of the decade scientists will have discovered a cure for influenza.
I will phone at six o’clock. He will have got home by then.

or looking "back" from the present:

Look at the time. The match will have started.
It’s half past five. Dad will have finished work.

We use would have as the past tense form of will have:

I phoned at six o’clock. I knew he would have got home by then.
It was half past five. Dad would have finished work.

We use would have in past conditionals to talk about something that did not happen:

If it had been a little warmer we would have gone for a swim.
He would have been very angry if he had seen you.
 

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Comments

hello Kirk & Peter
I've come across a sentence that i can understand with the grammar above
the sentence is : My own preferences, for example, have changed over the years - I would never have watched news programmes when I was younger.
could you explain that
regards

Hello Rezaya,

We're happy to help you, but could you please ask a more specific question? Which part of the sentence do you not understand?

All the best,
Kirk
The LearnEnglish Team

here in the sentence; I WOULD never HAVE WATCHED news programmes
"WOULD HAVE " is not "past conditional" here I suppose, so it must be the past tense form of "will have" ?

Hello Rezaya,

This sentence looks to me like a past conditional form describing an unreal situation in the past but. The condition (the if-clause) is not stated so is either implied or is clear from the context in which the sentence is used. For example:

I would never have watched news programmes even if I had had a TV. [I did not have a TV, but having one would not have changed my non-watching habits]

 

I would never have watched news programmes if there had been something else to do. [There wasn't anything else to do, so I watched news programmes]

 

I would never have watched news programmes if I was in your situation. [the other person watched news programmes; the speaker would not have done so]

 

Best wishes,

Peter

The LearnEnglish Team

hi Peter
you are right , thank you so much
the text is :
While toddlers might watch programmes about talking animals, teenagers prefer action and adventure or sports, and as adults we start taking an interest in news and politics. My own preferences, for example, have changed over the years - I would never have watched news programmes when I was younger. I think it would be very strange if our vitewing habits didn't mature!
if must be implied , and the sentence means that he changed his habit and start watching news!
that was not vivid for me :)
sorry but my another question is that, this text does not say that he still watch news or not. we can not find it out from the text. am I right?

Hello Rezaya,

The text doesn't explicitly state that this person still watches the news, but it does imply it. When they say 'have changed over the years', the present perfect shows that these changes began in the past but are still affecting the present. It's not completely clear -- it could be that this person doesn't watch the news now, or it could be that he or she doesn't, though I'd assume that he or she does.

All the best,
Kirk
The LearnEnglish Team

Hi)
There is an example about the match: "Look at the time. The match will have started". But why we cannot put "has started" instead of "will has started" there? I don't really see the difference.
Would you be so kind to explain this to me?

Hello ShannonSK,

Without knowing the context, I can't say for sure, but this sounds like something that someone who isn't at the match would say. For example, imagine our friend Ivan is playing an important tennis match at 12.00 and we promised him that we would go to watch him play. It's now 12.10 and we are still drinking tea in a café, so I could say 'Look at the time! The match will have started.'

In this case, 'will have' signals that I suppose the match has started, but I'm not completely certain because I'm not there and can't see any evidence of it. I could also say 'It has started', but by using 'will have started' I'm showing that I'm not completely sure. It doesn't necessarily show that I doubt the match has started -- it merely shows that I don't have any evidence for it. Most of the time, this is unimportant, but for whatever reason we can use 'will have' to show this shade of meaning.

If there was a television in the café and the match was on, then it would be incorrect for me to say it will have started, because the evidence that it has started is in front of me on the TV.

I hope that helps you make sense of it.

All the best,
Kirk
The LearnEnglish Team

Sir, I met my friend at a place where my another friend did not come but we had invited him, then we went to his home and after reaching there, I saw him doing his home work and I said " oh I thought you 'were or would be' sleeping But You are doing your home work, Nice." Now Suppose I did not go to his home, the what would be the best way to predict about him in present from these two options only "He would be sleeping or He would have been sleeping" and We had invited him yesterday but he did not come but I don't know why yet so what should I use for supposition from these two only "He would be sleeping yesterday or He would have been sleeping yesterday" and what is the difference ?

Sir, I met my friend at a place where my another friend did not come but we had invited him, then we went to his home and after reaching there, I saw him doing his home work and I said " oh I thought you 'were or would be' sleeping But You are doing your home work, Nice." Now Suppose I did not go to his home, the what would be the best way to predict about him in present from these two options only "He would be sleeping or He would have been sleeping" and We had invited him yesterday but he did not come but I don't know why yet so what should I use for supposition from these two only "He would be sleeping yesterday or He would have been sleeping yesterday" and what is the difference ?

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